Restricted or dirty flue
The most common cause by far. As creosote builds up inside the flue, the internal diameter narrows and gases struggle to escape. The result is smoke pushing back into the room when the door is opened — or during normal burning.
Blockage at the top of the flue
Bird nests, fallen leaves, possum debris, or a damaged cowl can cap the top of the flue entirely. This is especially common at the start of winter, after the heater has been unused for months.
Damp or unseasoned firewood
Wet wood burns at a lower temperature, produces more smoke, and accelerates creosote build-up — which then causes its own draw problems. Properly seasoned hardwood (12+ months) makes a real difference, especially in Tasmania's humid winters.
Negative house pressure
Modern homes are increasingly airtight. A running rangehood, bathroom exhaust fan, or even a clothes dryer can pull air out of the home and reverse the flue's draught. Cracking a window near the heater often confirms it.
Cold flue on start-up
On a freezing Tasmanian morning, a cold flue can briefly struggle to establish a draught. A small “priming” fire of kindling — door open at first — usually fixes it. If it keeps happening, the flue may also need cleaning.
Worn door seal or baffle
A perished door rope or a slipped baffle plate disturbs the airflow inside the firebox. This often shows up as smoke spillage combined with a heater that won't reach temperature.
A note on safety: chimney and flue issues can become serious quickly. When in doubt, leave the heater unlit and call a qualified sweep — a short visit beats guessing.